The new technique, photoelectroanalytical chemistry, will be further developed. This analytical system uses light to induce electrochemical current in the presence of a particular molecule or its derivatives, tris(2,2 feet-bipyridyl) ruthenium (RuL32+). It currently possesses low detection limits and suffers from little interference from serum constituents with the exception of large quantities of protein. The aims of the proposed research are to understand and defeat the limitations of the title technique, namely noise and protein interference, and to further exploit the remarkable chemistry of RuL32+ for trace organic detection. The ultimate goal of the proposed research is the development of reagentless immunoassay, a "probe" detector of drugs and hormones which will allow real-time hormone concentration measurements in biochemical measurement systems and body fluids.